An investigation of the chronic effects of mood-elevating stimulants which are commonly abused (amphetamines and cocaine) is proposed which will concentrate on neurochemical changes in the central nervous system, and especially in the basal ganglia. Neurochemical evidence for such phenomena as tolerance (and "reverse tolerance"), dependence and withdrawal, will be examined using both in vivo and in vitro assays for assessing synthesis and turnover rates of serotonin, dopamine and GABA, receptor binding for dopamine and GABA, and concentrations of substance P and met-enkephalin.